Electric circuit



Nov. 2 1940. A. BQ QMAN' 2222,95:

ELECTRIC C IRCUIT Filed Aug. 15, 1939 Patented Nov. 26, 1940 UNITED STATES PATENT OFFICE nuzc'rmo CIRCUIT.

Application August 15, 1939, Serial No. 290,211

8 Claims.

This invention relates broadly to electrical systems, in which conductors in difierent circuits are so arranged that unavoidable impairment of the insulation between conductors may produce intercoupling between difierent circuits, and a broad object of the invention isto prevent such intercoupling from resulting in response to such impairment of the insulation.

The impairment of the insulation referred to frequently occurs when bare portions of the conductors in different circuits are in contact with solid insulating material exposed to moisture. The leakage path is along the surface Off the insulating material, wires covered with suitable insulation showing low leakage through the insulation under moist conditions.

A particularly common source of trouble from current leakage in electric signaling apparatus for use in the field, is in multiple connectors employed to complete two or more distinct signaling circuits; the insulating surfaces of such connectors may become coated with dust or mud, which, when wet, has a relatively low resistance.

In accordance with the present invention, I prevent intercoupling of circuits through leakage across the insulation surfaces separating conductors in the difierent circuits by breaking the insulation leakage paths between conductors with a neutral conducting element, the latter efiectively preventing the setting up of leakage current between conductors of difierent circuits, although it cannot prevent leakage between the conductors of each individual circuit. It is to be understood, however, that in many circuits substantial leakage between the two conductors of a single circuit can be tolerated, whereas leakage between the conductors of different circuits cannot be tolerated.

The invention will now be more clearly explained by describing in detail some particular embodiments of the invention, as disclosed in the drawing, it being understood that these particular embodiments serve as examples only, and that numerous variations from the specific structures shown may be made without departing from the invention.

Inthe drawing: Fig. 1 is a longitudinal sectional view through a multiple circuit connecting plug, in accordance with the invention;

Fig. 2 is an end view cross section, taken in the plane IIII of Fig. l;

Fig. 3 is a perspective view of a multiple blade 5. and

Figs. 4 and 5 are circuit diagrams illustrating the theory of operation of my invention.

Referring first to Figs. 1 and 2, the plugconnee-tor therein disclosed comprises a male member I and a female member 2 connected to the 5 ends of wires 3 and 4, respectively, which are to be interconnected by engaging the plug members I and 2.

The male plug member I comprises a housing or shell 5 which is open at both ends but is pref- I erably constricted at the rear end to define a relatively small opening through which the wires 3 enter. The orifice at the small end may have an insulating-bushing 6 therein to protect the wires 3 from mechanical abrasion. Mounted within the 5 shell 5 near the forward end thereof is a metal partition 1 which may be secured in position within the shell 5 by screws 8. This partition I has insulatingly supported therein a plurality of contact prongs 9, I0, I I and I2, respectively, which prongs are connected at their rear ends to different ones of the wires 3. Each of the prongs 9 to I2, inclusive, may be insulatingly supported in the metal partition I by an individual bushing I3 of insulating material, which bushings are fitted .25 snugly in apertures provided therefor in the partition I.

Positioned rearwardly of the partition I is a second metal partition I4 which may be similarly mounted within the shell I by screws I5. This 30 partition I4 has apertures I6 therein, each dimensioned to pass one of the insulated wires 3. Each ductor I'I surrounded by insulating material I8 which may be rubber or other suitable insulating 35 material. The insulation I8 of each of the wires 3 preferably fits snugly within its associated aperture I6 so that the metal plate I I makes good electrical contact with the exterior surface of the insulation I8. o

- The female connector member 2 is substantially identical with the male member I, excepttha-t the connector elements 2t are in the form of split sleeves adapted to engage the prongs 9, I0, I I and I2 when the two members are pressed together. Furthermore, the conductive block or partition 2I which supports the prongs 20, extends beyond the end of :the shell 22 of member 2 so that it can enter into the open end of theshell 5 when the 50 members are pressed together.

In the female member 2 as illustrated in Fig. 1, there is no partition corresponding to the partition member I4 of the member I. It is to be understood, however, that such a partition may be and is preferably employed in the member 2 as well as in the member I.

The plug construction disclosed in Figs. 1 and 2 differs fundamentally from prior multiple-circuit connector plugs known to me, in that the connector prongs are insulatingly supported by the bushings l3 in the conductive plates 1 and 2|, whereas heretofore the entire partitions or plates. corresponding to plates 1 and 2| were made of insulating material.

With the former construction, if the surface of, the insulating material between the prongs be-' came coated with dust, mud, water or other Icon-fl ductive material, leakage paths were frequently set up between the prongs conn'e'cted'in different, circuits so as to cause objectionableintercoupling: between such circuits. If the different circuits were telephone circuits, then the intercoupling resulted in cross-talk, conversations over, one circuitbeing heard on the other circuit. However, such intercoupling' is objectionable in many signaling circuits other than telephone circuits, and the invention is in no sense limited to use in telephone circuits, although for convenience in description, telephone circuits will be discussed.

With the construction shown in Fig. l, intercoupling between the connector prongs connected to different wires as the result of leakage across the surface of the insulation elements I3, is prevented by virtue of the fact that all leakage paths between the different connector prongs are intercepted by the metallic wall 1, the resistance of which is negligible. Hence all leakage paths from all of the connector prongs terminate ata single point of common potential, and no potential difference can be set up in any of thesignaling circuits as the result of leakage from one or both conductors of another circuit.

This operation can be more readily explained with reference to the schematic circuit of Figs. 4 and 5. In Fig. 4, two independent telephone circuits 25 and 26 are disclosed, the circuit 25 including a pair of line conductors 21 and 28, respectively, and the circuit 26 including a pair of line conductors 29 and 30, respectively. For simplicity, these telephone circuits are illustrated as one-way circuits, each circuit having a microphone 3| 'connected thereto at one end through an induction coil or transformer 32 and. having a telephone 33 connected to the opposite end.

Let it be assumed now that at some point in-, termediate their ends the four conductors 21, 28, 29 and 30 pass through a plug connector'of'the type shown in Figs. 1 and 2, in which for convenience it may be assumed that'the line con-' ductor 21 is completed through the prong 9 (Fig. 2); the line conductor 28 through the prong 19; the line conductor 29 through the prong II; and

.the line conductor 30 through the prong l2; 'Assume, further, that the insulating bushings l3 have their exposed surfaces coated with conductive material, such as mud, so that the insulation is imperfect. Thus there maybe formed a leakage path represented by the resistances 35 and 36 between conductors 21 and 29 and a second leakage path represented by resistances 31 and 38 be tween conductors 28 and 30. However, both of these resistance paths are intercepted by the metal partition 1 so that the junction point of resistances 35 and 36 and resistances 31 and 38 are always at the same potential. By virtue of this fact both conductors 21 and 28 of circuit 25 nected by the unavoidable leakage paths to a point of common potential and different potentials cannot be applied to the two sides of either circuit by leakage from the other circuit.

On the other hand, it will be readily observable from an inspection of Fig. 4, that if the metallic interconnecting partition 1 were eliminated, a potential could be applied from conductor 28 to conductor 30 through the resistances 31 and 38 and from the conductor 21 to the conductor 29 through resistances 35 and 36, thereby creating a condition of cross-talk.

"In the case of two metallic circuits as in Fig. 4, it is necessary to create two leakage paths from two points of different potential in one circuit to two points of different potential in the other circuit." However, in many instances independent circuits are provided with a common ground connection so that it is only necessary to create one leakage path between one point in one circuit and "another point in the other circuit in order to intercouple the circuits- Thus in the circuits of Fig.5, two telephone circuits 40 and 4|, respectively, are equipped with transformers 42 and 43, respectively, the midpoints of which are grounded. With such an arrangement, it will be readily observable thatv a leakage connection represented by two resistances 44 and 45 in series between one side of circuit 40 and one side of circuit 4|, will suffice to intercouple the two circuits and produce cross-talk. However, if the junction point of the two resistance paths 44 and 45 is connected to ground, as shown, then this junction point is maintained at the same potential as the central taps of the transformers 42 and 43 and no potential can beintroduced into either circuit from the other.

To simplify the explanation in connection with Figs. 4 and 5, only a portion of the leakage paths has been illustrated. Actually, in practice, in-

addition to the leakage paths shown in Fig. 4, there would be a leakage path from conductor 21 to conductor 30 and from conductor 28 to conductor 29. However, all these leakage paths are intercepted by the partition 1. Similarly in Fig. 5 there might be leakage paths from each side of the circuit 40 to both sides of circuit 4| but all such leakage paths would extend through .a point of common potential represented by the partition 1.

Of course it will be understood that if the resistances of the leakage paths from each conductor of one circuit to both conductors of the other circuit were exactly the same, there would be no resultant cross talk and there would be no need for the present invention. However, in practice the different leakage paths are practically always of different resistances so that the resultant effect may be correctly represented by the diagrams of Figs. 4 and 5.

Heretofore the connectors disclosed in Figs. 1 and 2 have been described as consisting of four connecting members in four line conductors cor-' responding to the four line conductors shown in Figs. 4 and 5. When the system consists of two ungrounded metallic circuits, as shown in Fig. 4, the partitions 1 and 2| need not be grounded. However, when a grounded system as shown in Fig. 5 is employed, then the partitions 1 and 2| should be grounded and a ground wire 41 may be employed connected to a prong 4B which-"is mounted directly in the partition 1 and not insulated therefrom. Prong 48may cooperate with a sleeve 49 in the female member 2, which sleeve 49 is-rnounted directly in and electrically connected to the partition 2|.

Heretofore the only leakage paths discussed in connection with the structure shown in Figs. 1 and 2, are those which exist' across the sur- I faces of the insulating bushings 13. These are the most important leakage paths because they are usually relatively short. However another surface leakage path can exist on the insulated wires and it is to prevent circuit coupling as a result of such leakage that the partition 14 is provided. Such a leakage path may be traced as follows between the wires connected to the prongs II and I2, respectively:

From the bare end of the wire I! connected to prong ll, over the surface of the insulation IS on that wire to a point 50 where the insulation of the wire referred to is in contact with the exterior surface of the insulation on the wire connected to prong l2, and thence back over the surface of the insulation on the latter wire to the wire itself, this path being indicated in Fig. 1 by the dotted line 5|. However, since the insulated wires all pass through apertures in the metallic plate 14 and are in intimate contact therewith, the leakage paths are all short circuited by the partition l4 and the latter is preferably connected as by a wire 53 to the partition 1. Therefore all of the leakage paths, both those existing across the surfaces of the bushing l3 and those existing along the surfaces of the insulation [3 on the wires ll, are intercepted by a common conductor of negligible resistance.

As previously indicated, the present invention is applicable to other apparatus than telephone connectors of the type disclosed in Figs. 1 and 2. As one other example, a multiple knife switch is shown in Fig. 3. This switch comprises a plurality of movable blades 60 and associated contacts Bl adapted to be connected in difierent circuits. Each blade 60 and associated contact 6| are mounted upon a common base 62 of insulating material and the different bases 62 are interconnected by bolts 63 extending therethrough. However, the different bases 62 are separated by metal laminations 64 which intercept all leakage paths between the bases. These laminations 64 are preferably interconnected to each other and to the connecting bolts 63 by a conductor 65 of low resistance so that all are maintained at the same potential.

The operation of the switch shown in Fig. 3 to prevent intercoupling between different circuits incorporating different ones of the switch elements 60 and M, will be readily understood from the previous detailed description with reference to Figs. 1, 4 and 5.

Although as previously indicated certain specific forms that the invention may assume have been described in detail for the purposes of explanation, the invention is in no sense limited to the exact form shown, but is to be limited only to the extent set forth in the appended claims.

I claim:

1. In electrical apparatus including a plurality of signaling circuits, conducting elements in the separate circuits bridged by solid insulating material that is subject to current leakage under some conditions, neutralizing conductive means interposed between said conducting elements and separated therefrom by said insulating material, said conductive means interrupting all leakage paths of said insulating material between said conducting elements, and means for maintaining said neutralizing conductive means at a neutral potential with respect to said circuits.

2. In electrical apparatus including a plurality of signaling circuits, conducting elements in the separate circuits bridged by solid insulating material that is subject to current leakage under someconditions, at least one of said signaling circuits including two of said conducting elements, and neutralizing conductive means interposed between the conducting elements in different circuits and separated therefrom by said insulating material, said neutralizing conductive means interrupting all leakage paths of said insulating material between the conducting elements of different signaling'circuits.

3. In electrical apparatus including a pair of metallic signaling circuits, each circuit including two conductors, a conducting element in each conductor, said elements being separated from each other by solid insulating material that is subject to current leakage under some conditions, and neutralizing conductive means interposed between said conducting elements and separated therefrom by said insulating material, said neutralizing conductive means interrupting all leakage paths of said insulating material between the conducting elements in said two metallic circuits.

4. In electrical apparatus including a pair of independent signaling circuits having a common neutral connection, conductors for said separate circuits including conducting elements separated from each other by solid insulating material that is subject to current leakage under some conditions, and neutralizing conductive means interposed between said conducting elements, said conductive elements interrupting all leakage paths of said insulating material between the conducting elements in said independent signaling circuits, said neutralizing means being connected to said common neutral connection.

5. Connector means for completing conductors of a plurality of separate signaling circuits, comprising a pair of conductive contacting elements in each conductor of each circuit, solid insulat ing material for supporting said contacting elements in spaced relation to each other, said insulating material being subject to current leakage under some conditions, and neutralizing conductive means interposed between the conductive contacting elements of separate signaling circuits.

6. Connector means comprising a pair of frame members, one of said frame members having a plurality of conductive contacting elements and the other frame member having a plurality of cooperating contacting members, the contacting members on the two frame members being adapted to complete electrical connection in response to movement of said frame members together, in which each frame member comprises a plurality of insulating members each supporting one of said contacting elements, and supporting means of conductive material supporting said insulating elements and extending therebetween.

'7. Electrical connector means for completing conductors in a plurality of independent circuits, comprising a plug member and a cooperating socket member, each of said members having a plurality of electrical contacting elements and insulated conductors leading from said respective conductor elements, in which each member includes a plate of conductive material having separate apertures through which said separate insulated conductors extend.

8. Electrical conductor means comprising a frame, a plurality of electrical conductor elements of conductive material, an insulating bushing supporting each conductor element, a common conductive member supporting and being in electrical contact with all of said insulating bushings, a plurality of insulated conductors each connected to one of said conductor elements,and a conductive member supporting an insulated portion of each conductor in spaced relation from the other conductors, the portions o1 said insulated conductors between said contactor elements and said plate being in spaced relation to each other.

ARTHUR B. NOMANN. 

